Research in the Saline Wetlands

Salt Creek Tiger Beetle

Various projects have been conducted regarding the Salt Creek tiger beetle (SCTB). Such research includes: soil-slope preference, field collection and rearing, insecticide poisoning, light pollution effects on the beetle, and prey-based experiments. These studies are being conducted by the School of Natural Resources at the University of Nebraska-Lincoln (UNL).

Soil-slope preference study: Using optimum salt concentrations previously determined, a study was conducted to determine the egg-laying preference by female Salt Creek tiger beetles as to whether they preferred sloped (simulating the banks of Little Salt Creek) or flat (simulating original habitat 100+ years ago) soil. The results have been inconclusive.

Field collection and rearing: From 2007 to 2010, adult SCTB's were collected from the field and held in a lab for two weeks in order to produce larvae. The females were held for two weeks to produce eggs. Reproductive success varied depending upon collection circumstances, such as weather, in capturing fecund females. Beyond the issue of collecting fecund females, the most important conclusion drawn from this data is that the ovipositional substrates and other egg laying criteria are acceptable. For more information on the field collection and rearing study that took place between 2007 and 2010, see the SCTB Research section of the 2010 Progress Report.

Insecticide poisoning study: Using another salt-flat endemic tiger beetle (C. circumpicta), larvae were exposed to technical grade bifenthrin (Talstar®), imidacloprid (Gaucho®), and glyphosate (Roundup®) in various concentrations. These chemicals are frequently used in both agricultural and urban settings and SCTB adults and/or larvae may be potentially exposed to these chemicals in nature. No negative impact at concentrations which tiger beetles would be exposed to was found.

Light pollution: A study, as part of a Master's Thesis project, was conducted to determine the light sources tiger beetles are attracted to, and if ecological light pollution affects their oviposition success. Using a center chamber with tubes to six different light choices, he determined the beetles preferred in decreasing order; blacklight, mercury vapor, compact fluorescent, incandescent, and high pressure sodium vapor. Allgeier also found that gravid females distracted by light ecological light pollution may not lay as many eggs, likely reducing the number of offspring in the next generation. Females lay their eggs at night during a 4-6 week period. Disruption of normal nocturnal behavior, such as increased light pollution, has the potential to impact tiger beetle populations by attracting beetles out of their habitats and making them susceptible to mortality. (Allgeier, William J. "The Behavorial Ecology and Abundance of Tiger Beetles Inhabiting the Eastern Saline Wetlands of Nebraska." MS Thesis, 2005. University of Nebraska-Lincoln. May 2005).

Prey-based experiment: Washers, 1 ½" in diameter (to simulate a mature tiger beetle larva's strike distance) were covered in sticky trap and placed at 1 meter intervals from the water's edge to near the top of the bank along Little Salt Creek and left for 24 hours. Washers were collected and insects identified to the family level. The experiment ran at two week intervals from April through September, except during the time when adult SCTB were active (to avoid injury to SCTB). Analysis is not complete, but concentrations of insects tended to be much higher near the water. This experiment may be repeated in the future.

UNL hydrologists installed and continuously monitor wells throughout the Little Salt Creek watershed in order to better understand the local groundwater-flow dynamics. Each well is sampled for temperature, conductivity, pH, dissolved oxygen, cations, anions, and isotopes. A total of 28 wells have been drilled at various depths at several of the saline wetland locations.

In 2010, electrical resistivity measurements were taken at Whitehead Saline Wetlands and Little Salt Creek WMA. Using Electrical Resistivity Imaging (ERI), will provide the hydrologists with an expanded understanding of groundwater distribution through the acquisition of a large number of resistivity measurements collected at the surface.

Geophysical surveys were taken in-stream on Little Salt Creek near north 27th St. and Arbor Road. The distribution of surface resistivity measurements can be displayed in cross-section, and groundwater flow can then be inferred. Using piezometers installed in Little Salt Creek, measurements of electrical conductivity values were collected from the small diameter observation wells. These measurements will help correlate resistivity measurements with electrical conductivity values of groundwater at these sites.

Data from ERI images, electrical conductivity measurements, and bore logs have shown distinct plumes of saline water, migrating below the surface and discharging into local streams. With additional analysis, UNL hopes to develop an understanding of the complicated three-dimensional pathways that saline groundwater takes to surface water channels. The future plan is to begin looking more closely at the chemistry and hydrology of the springs in Little Salt Creek.

Soils

The Natural Resources and Conservation Service (NRCS) initiated field investigations at the Arbor Lake Complex using an Electro-Magnetic (EM-38) sampling device in 2009 and continued with the project in 2010. The device is useful for mapping variations in soil salinity and moisture content. Further EM-38 data collections may be conducted at other saline wetland sites in the future. The Electro-Magnetic sampling results for Arbor Lake can be seen here.

Sampling pits were dug at two saline wetland areas in 2009. The sample analysis was conducted by the National Soil Survey Laboratory (through NRCS) and is pending full characterization, which will be available in 2011.

Plant Communities

An inventory of saline wetland plant communities on SWCP properties began in 2009. The inventory provides baseline data on the extent and condition of existing saline wetlands from which future changes in saline wetland areas and their condition can be monitored. This ground-based plant community inventory provides valuable data for further analysis of saline wetlands, including saline species population studies and threat assessments.

The study is being conducted with funding provided through an agreement between The Nature Conservancy and the Lower Platte South NRD. Plant assemblage has been completed on Arbor Lake Extension (Anderson Property), Allen Parcel, Little Salt Creek West WMA, Warner Wetlands, and Little Salt Fork Marsh Preserve.

The inventory of most of the areas was restricted to lowland areas displaying saline soils to prioritize wetland plant communities. The table seen here identifies native plant communities in acres for the areas. An example of the plant community mapping for the low areas of the Allen Parcel can be seen here.